THE EFFECT OF METAL CONTAINING LIGANDS ON THE METAL-METAL QUADRUPLE BOND: STRUCTURE, SYNTHESIS, AND PHOTOPHYSICS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Christopher Blair Durr Graduate Program in Chemistry The Ohio State University 2015 Dissertation Committee: Dr. Malcolm H. Chisholm – Advisor Dr. Claudia Turro Dr. Patrick M. Woodward Dr. Hamish Fraser Copyright by Christopher Blair Durr 2015 Abstract The world’s ever increasing demand for fossil fuels has lead to a renewed focus by the scientific community to develop energy sources that are clean, renewable, and economical. One of the most promising emerging technologies is photovoltaic cells that can turn sunlight directly into energy or into fuels such as methane or hydrogen. In order for these cells to replace preexisting energy sources, it is necessary to increase their efficiency and processability while also curtailing cost. The focus of this work will be on electron donating materials, the main purpose of which is to absorb light and cause charge transfer to occur in the cell. To increase efficiency of donor materials several factors must be considered. Firstly, the material must capture as much of the solar spectrum as possible, which ranges from 400 nm to well over 1200 nm. Thus a material that has a broad, tunable absorption band is key to capturing as much of this light as possible. Secondly, the absorbing material must efficiently absorb photons by having a high molar absorptivity. Lastly, when light hits the donor material there must be a sufficient separation of the electron-hole pair. The material must stay in this charge separated state long enough to undergo charge transfer to an acceptor and thus begin the circuit. M2 quadruply bonded complexes, where M2 = Mo2, MoW or W2 have optical properties ideal for electron donating materials. Compounds of this type have a fully allowed metal- ii to-ligand charge-transfer (MLCT) band that is tunable from 400 nm to 1200 nm based on the choice of metal and ligand. This absorption is quite intense with extinction coefficients from 20,000 to nearly 100,000 M-1cm-1. The MLCT is caused by the transfer of an electron from a M2δ orbital to a ligand based π* orbital. The molecule exists in this singlet MLCT state for 3 – 25 ps before intersystem crossing to either a 3δδ* or 3MLCT state lasting from 2 ns - >75 μs. This work will discuss the synthesis, characterization and photophysics of M2 complexes and their interactions with metal containing ligands. By using organometallic or metal- organic ligands it is possible to cover more of the solar spectrum as the metal containing ligands chosen also have allowable optical transitions that are possible to tune. The ligands discussed herein contain chromium, rhenium, and platinum which each have interesting photophysical properties of their own. In the initial chapters metal carbonyls of chromium and rhenium were studied as the CO infrared stretches served as markers to follow using femtosecond time-resolved infrared spectroscopy. The effect of additional metal d-orbitals on the molecules excited state dynamics was discussed in detail for these compounds. A theoretical study of M2-Pt acetylide polymers was also conducted to determine the electronic structure and optical properties of future materials. Isonicotinic N-oxide is investigated as a ligand for Mo2 systems and the resulting complexes are attached to solid state films consisting of TiO2, NiO and Indium-Tin oxide. Finally, the solid state packing of Mo2 halobenzoate complexes is discussed as molecules of this form tend to form interesting halogen- halogen interactions. iii To Sarah iv Acknowledgments It has been a long and exciting road to get to a point where I may finally write an Acknowledgment to this thesis. Forgive me in advance for any errors or omissions in this section of the work, as one’s English tends to atrophy after years of writing in third person. There are so many people that I need to thank, incredible individuals who have helped me get to where I am today. In many ways, the chapters that follow are as much theirs as mine. First and foremost, I need to thank my parents, Virginia and Robert, and my sister Stephanie for putting up with years of my pseudo-scientific endeavors. From messes in the kitchen to destroyed computers in the basement, they have always encouraged my curiosities. However, despite this curiosity, my growing passion for chemistry may have never fully taken form without the help and dedication of my first mentor, Mr. David Weaver. He found a way to make chemistry come alive in ways that few could. I can wholeheartedly say, after spending nearly my entire life in school, Mr. Weaver is without a doubt one of the finest educators I’ve ever known. Shortly after my first year at Kent State University, I met Dr. Scott Bunge and joined his lab as an Undergraduate researcher. Scott had a tremendous influence on my decision to v get a Ph.D., and he taught me a love for inorganic chemistry, particularly for synthesis and structure, which remains with me to this day. Everything I have accomplished in Graduate School stemmed from the head start I gained by working in his lab, and for that I am eternally grateful. My decision of where to attend Graduate School was, in retrospect, a simple one. I wanted to work for a leader in the field of inorganic chemistry, someone who would let me pursue my own ideas, and someone who was a great person. With those things in mind, Dr. Malcolm Chisholm was an easy choice. Malcolm has been every bit the mentor I expected him to be. He has always been there to guide me through the treacherous years of my Ph.D., all the while encouraging me to explore new ideas and possibilities. I am incredibly proud to have worked with him for the past five years and I hope to pass on everything he has taught me to generations to come. Even if I work every day for the rest of my life, I will never be able to repay him for all he’s done. There are several other people who have been incredibly helpful throughout my time at Ohio State. Dr. Vesal Naseri was instrumental early in my career for teaching me the finer points of synthesis and for many helpful discussions. Dr. Claudia Turro has been like a second advisor to me, and she was always there when I needed to bounce an idea around or get an opinion. Furthermore, Dr. Turro has always believed in me, and for that I can’t thank her enough. Finally, Dr. Judy Gallucci has taught me more about crystallography than I ever thought possible. She has been infinitely patient with me over the years and has introduced me to an incredible community of scientists. vi I cannot overstate how inspiring and helpful my colleagues, both in and out of the Chisholm group, have been to me. We have a saying in the group that goes, “You learn the most from your brothers and sisters,” and I believe that every bit of that is true. I could not have asked for a better group of people to learn and work with all of these years, and I would like to thank all of them, both past and present. In particular I feel it necessary to mention a few of them by name, as they had substantial contributions to this document. Dr. Samantha Brown-Xu did all of the fs-TRIR and fs-TA seen in this document. She also contributed greatly to Chapters 3 and 4, and her initial work on TiO2 was the inspiration for Chapter 6. Any photophysics I know, I know because of Sam. Dr. Thomas Spilker was responsible for all of the emission data, and ns-TA seen herein. Furthermore he conducted the synthesis for the crystal engineering in Chapter 7. Tom is an excellent synthetic chemist, left-fielder, and friend. While Dr. Sharlene Lewis, Vagulejan Balasanthiran, and Philip Young did not contribute directly to this work, they have all been a joy to work with. Sharlene and Bala are two of the finest synthetic chemists I’ve had the opportunity to meet and both are exceedingly fine people. It’s personally been a pleasure to watch Phil grow from someone constantly asking me questions to constantly answering mine. He’s an exceptional chemist both at the bench and in the classroom. Last but certainly not least, Dr. Bryan Albani who, without contributing any words to this dissertation, made it entirely possible through his support and friendship from our first day onward. I started this section with family and thus it feels fitting to end with family. It’s funny how family comes in many different guises. There are those we are born into, those we vii marry into and those we are adopted by. My best friend Mark Spillan is a member of the latter, and without him I surely wouldn’t be here today. My “in-laws”, Mike, Lorrie, Emily and Kyle have filled my life with more joy and laughter than I ever thought possible, and their support has meant the world to me. (Kyle and Emily deserve a bit of extra credit having edited my tortured writing, and trying in vain to explain to me when one is to use commas appropriately). This family is growing still with Stephanie, Jason and little Arianna, who certainly won’t stay little for as long as I’d like her to.